1. Technical Field
An apparatus is disclosed for selectively dispensing one or more of a plurality of liquids, in particular multiphase liquids. The multi-phase liquids can for instance be emulsions or dispersions containing solid particles, such as paints, pigment pastes, colorants, dyes, inks, and cosmetics. The disclosure also pertains to a method of preventing segregation of a multiphase liquid in a pump conduit of such an apparatus.
2. Background of the Related Art
As explained in US 2002/0195462, one fairly widespread type of dispensing machine comprises multiple reservoirs for colorant fluids, connected to a dispensing circuit. Each fluid product is drawn from its respective reservoir by a positive-displacement pump and delivered to a corresponding three-way two-position distributing valve. When the valve is in an inactive position, the fluid is returned to its respective reservoir through a recirculation duct. When it is necessary to dispense a pre-set amount of fluid, the valve is set to an active position so as to deliver the fluid from the reservoir to a dispensing nozzle.
US 2002/0195462 discloses a dispensing unit for a fluid dispensing machine comprising at least an inlet duct and an outlet duct for fluid products, connected to a variable-volume pumping chamber comprising at least one flexible wall. Two non-return valves mounted in counter-phase are located in the inlet and outlet ducts, respectively.
WO 2004/013036 relates to a circuit for dispensing fluids, in particular dyes, inks, paints and the like, which comprises pump means including a variable-volume chamber with at least one flexible wall. The pump means communicate with an output duct for dispensing the fluids. Two one-way valves are mounted in series in the output duct.
EP 1 908 510 A2 discloses a device for dosage of fluids comprising a colour circuit (numeral 1 in FIG. 1) a storage tank (2), “inside which a given base paint or colorant is contained, . . . . Departing from the storage tank is an intake pipe 3, which connects the storage tank 2 to the intake of a pump 4. The delivery of the pump 4 in turn traverses a delivery pipe 5 and reaches a three-way valve 6 electrically controlled by the automatic managing system (not shown). The function of the three-way valve 6 is that of dividing the flow that reaches the pump 4 between a dosage line 7 and a recirculation line 8, in this way guaranteeing the constancy of the flow that traverses the valve 6. In fact, if the needs of formulation require the flow directed to the dosage line 7 (and through this to the mixing container 9) to be smaller than the flow of the delivery of the pump 4, the three-way valve 6 directs the flow in excess to the recirculation line 8 and, through this, to the storage tank 2.”
Systems for simultaneously dispensing a plurality of different liquids typically have long conduits, e.g. flexible plastic tubes, between the pumps and a manifold where the liquids are actually dispensed. Some liquids, such as colorants containing high density pigments or particles or instable binder/solvent solutions and/or emulsions, that remain in the conduits for prolonged periods, e.g. when the dispenser is not used during weekends or when a particular liquid is dispensed infrequently, may segregate, eventually forming a sediment or liquid phase and/or resulting in changes in properties. Segregation is prevented or at least reduced when the liquid is recirculated.
It is an object of the present invention to provide a relatively low cost and compact system for recirculation of the liquids in dispensers.